In this type of Collector, the Absorber plate is encased in a flat, heat-insulated enclosure (Heat Insulation), which itself is closed off with a glass shield, called a Collector Glazing. Flat-plate collectors are usually not evacuated, thus allowing conductive and convective heat loss through the movement of air. Their production costs, and hence their price, are well below those of the more efficient Evacuated-Tube Collector.